IMPERFECTIONS IN METALSDOE-HDBK-1017/1-93Structure of MetalsThe important information in this chapter is summarized below.Microscopic ImperfectionsPoint imperfections are in the size range of individual atoms.Line (dislocation) imperfections are generally many atoms in length. Lineimperfections can be of the edge type, screw type, or mixed type, depending onlattice distortion. Line imperfections cannot end inside a crystal; they must endat crystal edge or other dislocation, or close back on themselves.Interfacial imperfections are larger than line imperfections and occur over a twodimensional area. Interfacial imperfections exist at free surfaces, domainboundaries, grain boundaries, or interphase boundaries.Slip occurs when a crystal is subjected to stress and the dislocations marchthrough the crystal until they reach the edge or are arrested by anotherdislocation.Macroscopic DefectsBulk defects are three dimensional defects.Foreign particles included in the prime material (inclusions) are mostcommon bulk defectGas pocketsShrinking cavitiesWelding or joining defectsMS-01Page 22Rev. 0
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